Conventional subbing chemistry has not proven totally effective on biaxially oriented polyester support, and thus, there is a problem of adhesion in the photoprocessor environment of aqueous coats of photographic emulsions to these highly inert polymer surfaces. Recent approaches to overcoming the challenges of subbing biaxially oriented polyester support have involved plasma treatments, UV treatments, and other surface modification techniques often combined with heating the support material and/or complicated subbing chemistry. Recent advances in subbing technology have shown promise for replacing a U-coat/gelatin sub system with a single subbing layer applied to a plasma treated biaxially oriented polyester support. This is described in more detail in U.S. Pat. No. 5,425,980 issued Jun. 20 1995 entitled, "Use of Glow Discharge Treatment to Promote Adhesion of Aqueous Coats to Substrate".
As described in U.S. Pat. No. 5,425,980, it has been shown that photographic emulsions may adhere to plasma treated support using gelatin sub and no U-coat, a single subbing layer containing a terpolymer and gelatin (as described in U.S. Pat. Nos. 4,695,532 and 4,689,359), or no subbing at all. The plasma treatment technology has enabled the coating of emulsions and gelatin based subbing layers directly onto biaxially oriented polyesters.
As described in U.S. Pat. No. 5,563,029, filed Apr. 3, 1995, there are some problems associated with mechanical strength and/or treatment process latitude for subbing layers coated directly onto energetically treated polyester support. In addition, subbing layers based on gelatin may exhibit sensitivity of adhesion to keeping conditions prior to adhesion testing. In U.S. Pat. No. 5,563,029 it is demonstrated that acceptable mechanical strength, wide treatment process latitude, and insensitivity of adhesion to keeping conditions can all be achieved by molecular grafting of amine reactive hardeners to an energetically treated surface of a biaxially oriented polyester support. Amine reactive hardeners and related compounds may present health and safety issues when coated as a separate layer. Thus, there is a need to provide a safe, simple, and effective process for achieving the results of good wet adhesion of emulsion to biaxially oriented polyester support.
U.S. Pat. No. 5,563,029 demonstrates the importance of having a sufficient amount of hardener at the energetically treated surface. The grafted hardener layer then links gelatin molecules (in the coated emulsion layer) to the treated surface. While this approach has been demonstrated by coating the hardener as a separate layer, it is not obvious that blending the hardener with gelatin in a single layer should be effective because of competition between hardener and gelatin for reaction sites at the treated support surface. On the other hand, coating the hardener and gelatin as a blend provides a safer coating operation and the resultant gelatin grafted support is safer to handle.
The difficulty with blending hardener and gelatin is well demonstrated by Work, III et al (U.S. Pat. No. 4,241,169 issued Dec. 23, 1980). Work, III et al find that gelatin/hardener blends do not produce good adhesion unless a water soluble polyester is added to the coating solution. The difficulty encountered by Work, III et al may arise from an inappropriate match of the surface chemistry of the treated support with the hardener employed.
The present invention provides a novel combination of gelatin and hardener blends and energetic treatment, applied to a polyester support. This combination is demonstrated for amine-reactive hardeners and results in good wet adhesion with desirable process improvements, namely, safer coating operation and a subbing formulation for which long-term storage and handling prior to emulsion coating is not a concern.